1. Field of the Invention
The present invention relates to an apparatus and method for attenuating luminance of a plasma display panel (PDP), and more particularly, to an apparatus and method for attenuating luminance of a PDP, through which degradation of picture quality can be prevented and power consumption can be reduced. The present application is based on Korean Patent Application No. 2001-70730, which is incorporated herein by reference.
2. Description of the Related Art
PDPs employ time sharing to display gray scales. In other words, a single frame is divided into a plurality of sub-fields, and a luminescent period (or a sustain discharge period) is adjusted for each of the sub-fields to display gray scales. When a video signal having a high-luminance component is continuously displayed on a PDP, picture quality is degraded, the life of the PDP is reduced, and power consumption increases.
In order to extend the life of panels and reduce power consumption, conventionally, an apparatus for automatically attenuating the luminance level of an image according to an input level is provided for PDPs.
FIG. 1 is a block diagram of a conventional apparatus for attenuating luminance which is provided for a PDP. Referring to FIG. 1, if RGB data having a linear characteristic is input, a frame average detector 110 including an adder 111 and a divider 112 detects an average luminance level of a current frame. More specifically, if RGB data is input, the adder 111 adds luminance levels of individual pixels to calculate the sum of luminance levels for a current frame. The divider 112 divides the sum of luminance levels calculated by the adder 111 by the number of pixels to calculate an average luminance level for the current frame. The number of pixels is the number of pixels constituting the current frame.
A sustain controller 120 determines the number of sustain pulses during the sustain period for the current frame according to the average luminance level calculated by the divider 112 and provides the determined number of sustain pulses to a PDP driver (not shown). The PDP driver includes an XY controller and a sub-field generator and adjusts the luminance level of an image displayed on the PDP according to the number of sustain pulses. The luminance of an image is proportional to the number of sustain pulses. Accordingly, the sustain controller 120 compares the average luminance level with a predetermined reference value. If it is determined that the average luminance level exceeds the reference value, the sustain controller 120 determines the number of sustain pulses, which will be generated, to be less than the number of sustain pulses which is set previously, and provides the determined number of sustain pulses to the PDP driver so that the luminance level of the image can be attenuated.
In order to compensate for a drawback that a large amount of calculation is required to add luminance levels of all of pixels included in an input frame, there has been provided a method of sampling luminance levels at proper intervals to calculate an average luminance level for a frame.
As described above, a conventional apparatus for attenuating luminance uses the number of sustain pulses that is determined based on an average luminance level calculated for each of frames. Accordingly, when an area that is too small to significantly influence an average luminance level for a frame has a high luminance level, the high luminance level of the small area cannot be lowered satisfactorily. Particularly, when a calculated average luminance level is low, as shown in FIG. 2, the luminance level of a small circular area 201 is rarely attenuated. In this situation, if the same pattern is continuously displayed on the small area 201 for a long period of time, picture quality on the small area 201 is degraded more quickly than on other areas.
To solve the above-described problems, it is an object of the present invention to provide an apparatus and method for attenuating luminance to prevent degradation of picture quality on a local area and excessive power consumption.
Accordingly, to achieve the object of the present invention, there is provided an apparatus for attenuating luminance of a displayed image. The apparatus includes a motion detection unit for detecting whether input data has motion, a duration check unit for checking a duration time for which the input data has no motion when the input data is detected as having no motion in the motion detection unit, an attenuation constant generator for generating an attenuation constant corresponding to a luminance level of the input data when the input data continuously has no motion for at least a predetermined period of time, and a level attenuation unit for attenuating the luminance level of the input data using the attenuation constant generated from the attenuation constant generator.
Preferably, the motion detection unit includes a memory for storing the input data in units of frames, an adder for detecting a difference between data provided from the memory and the input data, and a comparator for comparing the difference with a predetermined threshold value to detect whether the input data has motion.
Preferably, the duration check unit includes a timer which operates in response to a signal indicating the input data has no motion, and a comparator for comparing time information generated depending on the operation of the timer with a predetermined threshold value to determine whether the input data continuously has no motion for at least the predetermined period of time.
Preferably, the attenuation constant generator includes a level detector for detecting the luminance level of the input data, and a look-up table for storing a plurality of attenuation constants and providing an attenuation constant corresponding to the luminance level.
Preferably, the level attenuation unit includes a delay unit for delaying the input data; and a multiplier for multiplying the input data, which has been delayed by the delay unit, by the attenuation constant and outputting the data having an attenuated luminance level.
There is also provided a method for attenuating luminance of a displayed image. The method includes detecting a luminance level of input data; comparing a previous frame with a current frame in units of pixels or predetermined blocks; if a pixel unit or predetermined block unit image is determined as a still image, checking a duration time for which the pixel unit or predetermined block unit image is continued in a still image state; if the duration time is at least a predetermined period of time, determining an attenuation constant corresponding to the luminance level of the input data; and attenuating the luminance level of the input data using the attenuation constant.